This invention relates to e-mail transfer and, more particularly, to methods and apparatuses for controlling access to mail transfer agents by mail user agents and by other mail transfer agents.
The ever increasing prevalence of electronic mail (e-mail) poses significant challenges to industry and management of companies. Many important communications occur through e-mail. As a result, the need to manage the same is manifest. Failure to do so may have far reaching consequences including, but not limited to, huge financial losses. For example, a denial of service attack presents serious concerns for providers of Internet sites, because of the financial losses that may result.
Movement of e-mail messages typically occurs between a mail transfer agent (MTA) and a mail user agent (MUA), or between two different MTAs. To that end, a standard feature of all e-mail messages is its envelope, providing its originator and one or more recipients. One standard for defining for such an envelope is described by J. Klensin as “Simple Mail Transfer Protocol,” RFC 2821 (April 2001) (“RFC 2821”). RFC 2821 is the standard for the transmission of e-mail messages over the Internet. This protocol is commonly referred to as SMTP. One advantage of SMTP is that sender and recipient information is transmitted along with the mail message.
SMTP is used to enqueue an e-mail message to an MTA over a TCP/IP connection. Typically, a client or a remote MTA will establish a TCP/IP connection to the local MTA, use SMTP to send the envelope sender and recipient, and then the header and body of the e-mail message, and upon confirmation from the local MTA that the e-mail message has been successfully received, terminate the TCP/IP connection. In addition, multiple recipients may be specified for a single e-mail message. It is also possible for multiple e-mail messages to be sent during a single TCP/IP connection.
Two Internet mail protocols have bee developed for receipt of e-mail messages from an MTA by an MUA. One standard is known as “Post Office Protocol version 3” (“POP3”) and the other is known as “Internet Message Access Protocol version 4 revision 1” (“IMAP4rev1”). The POP3 standard is described by M. Rose in “Post Office Protocol—Version 3” RFC 1081 (November 1988) and “Post Office Protocol—Version 3 Extended Service Offerings” RFC 1082 (November 1988). This standard allows an MUA to connect to an MTA in order to check for new e-mail messages in the mail account being accessed by the MUA and to read header information.
Unlike the POP3 standard, the IMAP4rev1 standard does not require a client to download an e-mail message to a local directory of a client from the MTA in order to read the e-mail message. Rather, the IMAP4rev1 standard allows a client to perform the client's mailbox functions while the e-mail message is maintained the MTA. Specifically, upon receipt of an e-mail message, the MTA stores the message in a region of a database, referred to as a mailbox for, which is designated and typically may be accessed only by, the client to which the e-mail message is directed. The client is then notified that there is a new message. The features of IMAP4rev1 are described by in M. Crsipin in “Internet Message Access Protocol—Version—4rev1” RFC 2060 (December 1996).
An advantage provided by each of the aforementioned mail protocols is the support of public mailing, or distribution, lists. In this manner, a client may transmit, to a collection of individual client mail addresses, an e-mail message directed to a single address. This may be achieved by an MTA employing an automated mailing list manager that uses a mail exploder to turn a single identifier for a distribution list the collection of client addresses. Alternatively, the MTA may achieved the public mailing or distribution by forwarding a single e-mail message to the distribution list on the MTA that is accessible by all client members of the list. The MTA notifies the respective clients that a message is being retained. The public distribution lists for these systems are generally maintained by an administrator. The public distribution list poses a probability that a single client can consume the resources of the MTA by a single request to transmit a message.
Thus, there is a need for a system and method to provide improved control of access to MTAs by clients.